1. Field of the Invention
The present invention relates to a bump attachment method for bonding bumps to leads formed on a carrier tape.
2. Prior Art
Publications such as Japanese Patent Application Publication (Kokoku) Nos. 62-31819 and 62-34142 and Japanese Patent Application Laid-Open Publication (Kokai) No. 59-139635, etc. disclose methods for attaching bumps to leads provided on a carrier tape.
Such bump attachment methods are performed by means of a bonding apparatus such as that shown in FIGS. 5 through 7.
As seen in FIG. 5, a plurality of leads 2 (see FIG. 7) are formed in a given order on a carrier tape 1 made of a polyamide film, etc. This carrier tape 1 is supplied from a supply reel (not shown) and wound around a take-up reel (not shown) after passing through a first tape clamper 3, a bonding guide 4 and a second tape clamper 5. A tool 6, positioned above the bonding guide 4, is caused to move in the vertical direction (Z direction) and in the horizontal direction (X and Y directions) by a driving means (not shown). This tool 6 passes through a bonding window 4a formed at the center of the bonding guide 4. A camera 7 is installed above the bonding window 4a and detects the leads 2 on the carrier tape 1 and the bumps 13.
Installed beneath the bonding guide 4 is a bonding stage 10. This bonding stage 10 is moved in the horizontal direction (X and Y directions) and vertical direction (Z direction) and also rotated (.theta. direction) by a driving means (not shown). The bonding stage 10 has a vacuum chuck 11 on its upper end so that a substrate 12 made of glass, etc. is held (via suction force) by this vacuum chuck 11. As shown in FIG. 6, bumps 13 are formed on a substrate 12 at a fixed pitch in the lateral and longitudinal directions in device patterns 14a, 14b, . . . so that each of them corresponds to the leads 2 of one device pattern formed on the carrier tape 1.
A method for attaching bumps using the apparatus thus constructed will be described below. Since the leads 2 on the carrier tape 1 are omitted from FIG. 6, reference should be made to FIG. 7 whenever the leads 2 are mentioned.
The carrier tape 1 is fed when the tape clampers 3 and 5 are opened, and the leads 2 that are to be bonded are positioned under the bonding window 4a. Then, the tape clampers 3 and 5 are closed so that the carrier tape 1 is held securely. The positions of the leads 2 are detected by the camera 7 and stored in an arithmetic unit (not shown). The tape clampers 3 and 5 and the bonding guide 4 are moved in the X and Y directions so as to eliminate any discrepancy in the lead positions stored in the arithmetic unit. Thus, the horizontal positional discrepancy is corrected. Then, the bonding stage 10 is moved in the X and Y directions so that the bumps 13 in the device pattern 14a are positioned to correspond to the leads 2.
Next, the tool 6 is moved in the X and Y directions and lowered so that the leads 2 are pressed against the bumps 13 as shown in FIG. 7. As a result, the bumps 13 in the device pattern 14a are bonded as a group to the leads 2.
Afterward, the tool 6 is raised and moved in the X and Y directions, and then, the carrier tape 1 is fed a fixed distance so that the leads 2 in the next device pattern to be bonded are positioned beneath the bonding window 4a. The device pattern 14b that is to be bonded next is fed and positioned beneath the leads 2. Then, the action described above is repeated so that the bumps 13 in the device pattern 14b are bonded as a group to the leads 2.
In the prior art described above, since one device pattern consisting of leads 2 and one device pattern consisting of bumps 13 are aligned and then the leads and bumps are bonded as a group, the following problems arise:
Bonding is performed in groups. As a result, variations in the inclination of the tool 6 with respect to the bonding surface or in the thickness of the individual leads 2 and bumps 13, etc. may make it difficult to achieve uniform pressure bonding of the individual leads 2 and bumps 13 within the device patterns. Also, it is necessary that the bumps 13 be arranged on the substrate 12 in accordance with the arrangement of the leads 2. Moreover, in cases where defects occur within the device patterns (e.g., positional discrepancies of bumps, missing of bumps, presence of unnecessary bumps, etc.), the device patterns 14a, 14b . . . become unusable, resulting in that the yield drops.